Competing C-H and C-F bond activation reactions of a fluorinated olefin at Rh: a fluorido vinylidene complex as an intermediate in an unprecedented dehydrofluorination step.

Abstract

The hydrofluoroolefin Z-1,3,3,3-tetrafluoropropene has been activated via an initial C–F bond activation and subsequent C–H bond activation using [Rh(H)(PEt3)3] (1) or via C–H bond activation at [Rh(CH3)(PEt3)3] (8). In both cases the formation of [Rh{(E)-CF Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHCF3}(PEt3)3] (3) was observed. Importantly, the C–F activation product [Rh{(E)-CHCHCF3}(PEt3)3] (2) reacts in the presence of Z-1,3,3,3-tetrafluoropropene into 3. The latter converted into [Rh(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CCF3)(PEt3)3] (6) by an unprecedented dehydrofluorination reaction, presumably via a vinylidene complex as intermediate. When the carbonyl complex [Rh(CCCF3)(CO)(PEt3)3] (12) was treated with an excess of NEt3·3HF or HBF4 at low temperature, the formation of the phosphonioalkenyl compounds [Rh{(Z)-C(PEt3)CHCF3}(CO)(PEt3)2]X (X = F(HF)x, BF4) (13) was observed. The formation of 13 can be explained by an attack of PEt3 at the electrophilic α-carbon atom of an intermediate vinylidene complex. The employment of PiPr3 derivatives as model compounds allowed for the isolation of the unique fluorido vinylidene complex trans-[Rh(F)(CCHCF3)(PiPr3)2] (16), which in the presence of PEt3 transforms into [Rh(CCCF3)(PEt3)3] (6).